Airplane safety control system



Allg 14, 1956 T. A. FEENEY AIRPLANE SAFETY CONTROL SYSTEM 3 Sheets-Sheet l Filed July 3, 1952 x y E mw N 2 W V. M W4 M Q A.' 9 f f N M M /H N @MMM Sheets-Sheet 2 Aug- 14, 1956 T. A. FEENEY AIRPLANE SAFETY CONTROL SYSTEM Filed July 3, 1952 Praffar@ 'Ila fi ff9 ug- 14, 1956 T. A. Fr-:l-:NEY

AIRPLANE SAFETY CONTROL SYSTEM 3 Sheets-Sheet 5 Filed July 5, 1952 Elfi/0N 477467//145/1/7 United States Patent Oilice 2,758,806 Patented A ug. 14, 1956 AnzPLANE SAFETY coNrRoL` SYSTEM Thomas A. Feeney, Los Angeles, Calif., assignor to Northrop Aircraft, Inc., Hawthorne, Calif., a corporation of California Application July 3, 1952, Serial No. 297,049 17 Claims. (ci. 244--ss) The present invention rela-tes to full powered airplane controls and, more particularly, to a means and method of controlling large airplane control surfaces under power only, by a minimum exertion of force by the pilot of the airplane and wi-th a maximum of safety. This application is a continuation-impart of my prior application Serial Number 23,567, tiled April 27, 1948, and now abandoned.

In U. S. application, Serial Number 681,890, tiled July 8, 1946, since matured into Patent Number 2,582,348, dated January 1'5, 1952, l. K. Northrop and I described and claimed certain control surfaces suitable for all-wing airplanes, notably, those used on the U. S. Army bombers designated Ias the XB-35 and YB-49.

The full powered surface controls iof ythe XB-SS bomber are hydraulically operated under the applica-tion ofminimum stick force by the pilot, without control surface feed-back or feel being transmitted to the pilot, and the' present invention has for an object the provision of a means and method of obtaining full power operation of large airplane control surfaces, such as those used in the XB-35 and YB-49 for example, or in other large airplanes of the more conventional type. n

It is an object of the present invention to provide a safe means and method of operating airplane control surfaces under full power without normally transmitting force back to the pilot and with a simple mechanical unit that has minimum hunting characteristics. Y

With full power operation of the control surfaces, the applied pilot force'need only be nominal, and it is another object of the present invention to provide a full power operated airplane surface control where the force applied vby the pilot for operation thereof is of negligible importance, irrespective of the actual force required to move the control surface.

In the preferred embodiment of my invention, hydraulic motors are utilized with the pilots control element being connected directly to the -valve controlling the flow of hydraulic Aiiuid to the motor, as by cables for example. Asl it is possible for such valves to jam or bind in use dueto the entr-ance of foreign matter into the valve, care must be taken that such a valve jaw does not prevent the operation of the control surface by the pilot. In addition, in military airplanes cable connections are subject'to damage in action. p

Accordingly, it is another object of the present invention t-o provide a hydraulic full power attitude surface control system for airplanes that provides maximum safety under adverse operating conditions. j

By the use of the present invention, `a full power attitude control system `is provided achieving maximum safety lof operation without the necessity of resorting 4to a separate emergency system. In brief, the present invention includes the use kof two motors, each forexample of the cylinder and piston type, connected to move, when energized, the same attitude control surface .oan airplane. VvA `lluidl control valve is used on or near each motor to control lhydraulic fluid from a constant pressure source to energize the motor.v Each valve is connected by separate cables to the pilots control element, wheel column or stick, and a separate cr-oss connection control between the two halves is made adjacent the two motors; Thus if either cable connection from the pilots control element is broken, the undamaged cable connection will operate both valves, one directly and the other through the cross connection. In order to `prevent the jamming of one valve from immobilizing the other valve, a spring loaded connection is made between each valve and each cable connection to the pilots control element; these spring loaded connections also being between each valve and the cross connection between -the valves. The spring loading is made suiiiciently powerful so that in ordinary operation of the airplane, the ,connections from the pilots control element to the valves act as solid connections. lf, however, one valve should jam, the pilot can override the spring loading on the jammed valve to control the surface by the other valve. In addition, the system will operate with one jammed valve and with either cable connection to the pilots control element shot away.

The spring loaded connection at each valve can serve another important function: By proportioning the constant pressure of the source of hydraulic power with the piston size in the hydraulic-motor, the maximum force that can be applied to the surface by the system can be predetermined so that under air-loads that might kwell cause the hinge moments on the surface to exceed safe figures, the surface can reverse the mot-or thereby preventing damage to the surface. high air-loads on the surface are able to force the actuating cylinder and piston assembly back in reverse from the position being called for by the pilot-operated control valve, thus actually stalling and then pushing hydraulic fluid back through the pressurized cylinder port. As it is preferred t-o have internal valve travel less than the distance the pilot can move the control element, it would be possible for the valve to bottom in its casing thereby transmitting full surface-load to the pilot. Asjit is preferred that the cable connections between the valves and pilot be of minimum weight, such bottoming will override the spring loading and limit` the force feed-back to the pilot to the preload of the spring connections.

Other objects and advantages of the present invention will be apparent from a description of the appended drawings in which:

lFigure l is a diagrammatic plan view of one form of airplane to which the present invention may be applied.

Figure 2 is a diagram of the cable and motor assembly used to move the elevcns of the airplane shown in Figure l. n

Figure 3 is a perspective view of a pilots control column connected for elevon control.

Figure 4 is a perspective view of one preferred form of hydraulic motor power unity used for full power control of the elevons on the airplane of Figure l.

Figure 5 is a longitudinal sectional view showing a servo-valve construction suitable for use in the power unit of Figure 4.

Figure 6 is a perspective diagram of a motor unit suitable for rudder operation. y

Referring first to Figure l, the all-wing airplane shown diagrammatically is the .XB-35, having four reciprocative motors within the airplane driving pusher propellers 2,

' and having a wing spread of 172 ft. with a length of 53 ft.` The control surfaces for this y.airplane comprise outer trim flaps 3 on each wing panel 4 and ?A having separable drag rudders 6 mounted thereon, inner landing flaps 7, and intermediate elevons 8. All of-these control surfaces are full power operated by the pilot with l no pilot force whatever being applied to the control sur- That is, dangerously fac'es, and present invention will be described as applied'to the power means used for full power operation v1`1 cz 'are connected byseparate cables 15 and 15a to right inboard and outboard powerunits in the right wing 4 which is only partially shown. A cross cable connecti o1 i L is madebetween each of the left power units as shown, andsimilarly between each of the right power units. Thus each ofthe four power units is connected to be separ ately operated directlyy from the control quadrants at the controlcolumns with a cross cable connection between the power units connected to the same surface; The power units are connected to be operated in parallel on each elevon, and are operated together in the same direction for elevation control and in opposite directions for aileron` type control, thus giving rise to the termelevon. The elevons can be moved in this manner for example, by the constructionl of the control column as shown in Figure 3, which will next be briey described.

,A` control column casing as indicated by broken line yis mounted on a composite shaft comprising an outer tube 21 connected by linkage 22'to one cable quadrant 11a, and' an inner shaft 2'4 connected by another linkage 25 to the'other cable quadrant 11a'. Inside casing 20 a tube drum`27 is mounted ontube '2 1 and a shaft drum 29 is mounted on shaft 24, these drums being' of the same diameter and' cut away inthe figure for clarity.v A chain 30` is drivenby a sprocket 31 on one end of wheel shaft 32,"the'wheel shaft 32 extendinglout of casing 20 with a wheel34 mountedv thereon.

The ends of chain 30`are connected to chaincables 35; onepa'ssing about halfway' around tube drum'27 and then being: xed thereto, the'other passing similarly around shaft' drum 29L Thus when wheel 34H is rotated, oppositefmotiri'of4 cable quadrantsl 11ais obtained, and when the c`asing'20 is rocked forward'pr aft,'both` quadrants will move togetherfor elevator controll O pp'osedsprin'gs 37ar'e` attached tolevers 38attached to centering shaft 40 whichha'send drums 411thereon'conriectedpn oppfofsite sides'to' centering cables 42ione of' whichpasses around drum'27 and the other around drum 2 9 t' be a ixed thereto. Opposed springs 37 provide forces centraliz'ing wheel534`in a'prede'terrnined nutraliposition. The 'jcentr'aliZing system forelevator movement of the column isntf'shownbutmay b'zisimilrt. thatdSribe'd abgve, or may be ofaltype: applying an aerodynamic feel from a b ellowsactuated primarily by anair flow separate from the' controlled surface for example'1- I vre fe r next to Figure, 4, which shows'in perspective ViewI an installation of ahydraulic motor asfused to operate'an'elevori; A'vertical'axleAQis'placed within a wing panel, for example, and'pivotedto wing spar attachmentsSQ at'eachend thereof resp ti vely, by'short'bellcrank aims 51 and 52' resr'iectively'l.l Above, axle 49 carriesapulleyplate 54 extended to cross arms 55'carrying e'n'd pulleys 56 over which run contr o 1 cables 12 operatedV by the pilot from the control column 10 or 11. Cables 1 2 pass around tension box pulleys 57 to enter a cable tensioning box 58 attached to the pulley plate 54 as is Vwell known in in the art. Rotation of axle 49 by the pilot moves long bell crank arm 60 which is attached to a springloaded valve operating rod 61 passing through an aperture in the wing spar to link directly witha valve spool attachment 62.

Valve spool attachment 62 enters' a valve assembly 63 inserted in a valve block 64 securely fastened to one end of a hydraulic moto r cy linder 6 5, the o theijende of cylinder 65' being attached to an elevon operating arm (not shown) by elevon attachment 67. A hydraulic piston rod '70 enters cylinder 65 opposite elevon attachment 67 and is attached to the airframe by wing attachment tting 71. Piston rod 70 is, as is well known in the art, attached to a hydraulic piston 65a inside of cylinder 65.

Valve block 64 is provided with a hydraulic fiuidpressure inlet 72 and a Huid return pipel 74. Ihe'piston r'o'd end of the cylinderV 65 is supplied with fluid through the valve block, and the closed end of the cylinder is supplied through the block and through outside pipe 75. Referring again to Figure 2, the cross connection between power units 13 and 14 is created by cross connection cable L connected to an axle quadrant M on the end of axle 49 of one power unit 13 and to a similar axle quadrant M on the axle 49 of the other power unit 14.v ln

- each power unit, an idler cableN is attached at one'end thereof to an` axle quadrant M and passes around' an idler pulley O to return to an opposite axle quadrant P also mounted on axle 49. Thus when both cables 12 and 12a are intact, cross connection cable L merely idles. However, if either cable 12' or 12a is broken for any reason, both valve rods will still be driven,U one directly through cable 12 or 12tlg' the other indirectly through cross connection cable L. Thereare several preferred requirements for theoperation of the valve assembly 63, namely: there should be al neutral leakage' in the valve with a restricted flow increasing as the valve spool moves away from neutral, the valve should provide a preload on both sides of the piston' to resist movement ofthe surface away lfrom neutral due to air shock, vand the valve should be sensitive, thereby permitting the pilot to make small corrective movements of the control surface. Several typesof valves canv satisfy these requirements and ,one of them will be described'in vdetail herein, as shown in Figure 5'. This particular valve is` showngidescribed and claimed'by Parker in a copending application, Serial No.v 17,624, filed March29, 1948, now Patent No'. 2,631,571. In Figure 5, valve assembly 63, one end of which p rojects from valve block 64 in Figure 4, comprises a spool casing adapted to be fastenedfinto'valve'block `64 and an inner spool to' be moved by valve' operating rod not shown. The spool casingv starts at the left ofthegure. with a hollow spool slide end 8 2`followed by a barrel portion 83 of uniform outer diameter to termina-te in a threaded end 84:

The inner terminus of slide end,` 82 ifsl provided with opposed ports 85 eute'r'ing'ya return chamber 8 6whicl1 is separated from a slide chamber S7 in` this'" endfby a partition 8S bored out to pass'a" s p`ool rod18`9 attached outsideof' partition' 88 to' al` slide 90' in turn -attached to valve spool:atta'chment 62'. Slide 941 is hfeldyto'ka fixed' travel' by slidepin 9 1l attachedV tolslide' end' This pinl passes -through el'ongted hole 92T in the slide "l A spool' rod packing 9,3 isinstalledfin 'partitionfvS'SL spporrsd sa is tracht-,ahy speerpinlsfi fessi-66135 slidingl inside'of the' spool casin`g SpoolhpfiriV 94 isfin line with opposedports 85 for' easiy assembly. Spool will be described later,

on the eneide of die spesi asiiig, communicating withopposed ports 85, is af r`eturn fluid" groove 100', which, when" the valyel assembly is` in place in' valve block 64, communicates"witlifreturn'boreltll. Ah outer slide e'nd packing sealT 1612 isolates returnl Huid-l` groove from the'o'u't'si'de of th'e'valve bleek; I

To' the' right o'f th'ew return iluid groove 10'0 is an outer ring seal 103` separating'o'uter idireturnl'gioove 100 fronrone cylii'nder` chani'bergrodye 1M 'havingi circumferential' cylinderv` po'ts'10`5 therein' communicating with inner' cylinder chamber' groove 106 'fa'cingf'the lspool 95. Another' outer ring Sear 107', feuows, their *an 'dater pressure fluid groove 108comnicating:withtheinf teriorl-of the spool casing without an Ainner groovevfby pressure ports 109. f v

-The outer pressure fluid groove 108 connects through valve block 64 with pressure inlet 72 through pressure bore 110.

Next is still another ring seal 112 followed by a second outer cylinder chamber groove 114 connectingwith an inner second cylinder chamber groove 115 by circumferential return ports 116. A tifth ring seal 117 follows. Next comes the threaded end 84 with threads 118 sealed from the outside by threaded end ring seal Threaded end 84 is provided with a threaded end rc turn uid chamber 122 connecting with slide end return chamber 86 by threaded end ports 123, through a central spool bore 124 and slide end ports 125. These latter ports 125 connect with return groove 100, bore 101, and then return pipe 74 shown in Figure 4.

vBoth ends of spool 95 t are exactly alike, the spool being attached at the threaded end to a spool -idler rod 127 by idler pin 128. Idler rod 127 passes through the threaded end 84 and is sealed by idler rod seal 130 mounted in the threaded end. Asv the exposed areas at each end of spool 95 are the same, no piston effect is applied by the return fluid pressure.

Opposite pressure ports 109 leading to outer pressure lluid groove 108, the spool is cut away to form a circumferential fluid distributing groove 131 kextending equal distances, when the spool is in neutral position, on each side of pressure ports 109. This distributing groove 131 is provided with sides normal to the surface o1' the bore in which the spool slides, and a plurality of circumferentially distributed pressure bores 132 and 133 extend longitudinallyL in the ,spool wall from re.- spective sides of the pressure distributing groove 131 a suicient distance to terminate beyond the near sides of inner first and second cylinder chamber grooves 106 and 115 in the spool casing.

Both ends of the spool 95 are also cutaway opposite return uid chambers 86 and 122 to form shoulders which also have circumferentially spaced return bores 135 and 136 extending longitudinally into' .the spool 95 past the opposite sides of the inner rst and second cylinder chamber grooves 106 and 115 respectively.

The spool construction is completed by four sets 140e, 140b, 140e and 140e! of flow ,holes bored vnormal to the peripheral surface of the spool and entering the. various bore holes 132, 133, 135 and 136 respectively. These flow holes are bored with definite patterns with respect to the various inlets and outlets of casing and said spool. These ow holes are used to. pass 'all the uid flow through the valve, as slide pin 91 limits the travelof the spool to less than the travel required to open pressure groove 131 on the spool to either of the inner cylinder chamber grooves 106 or 115.

In Figure 5, the spool is shown in neutral position. The tiow holes 1401; and 140C nearest to the pressure inlet are arranged to be bisected by the more central shoulders of cylinder grooves 106 and`115. The ow holes 140g and 140d nearest the ends of the spool are also bisected by the outer shoulders of return ow grooves 106 and 115 respectively. Thus, in neutral position a small ow is constantly applying pressure-to both ends of cylinder 65 of Figure 4 through the centrally bisected ow holes. The uid then leaks to return through ow holes 14051 and 140d. Y

In one preferred form of valve,-a constant pressure of 2000 p. s. i. from a constant pressure source such as a controlled pressure pump driven by one of the engines of the airplane for example, is used in pressure inlet 72, and the bisected flow holes are proportioned to provide a pressure drop of 1000 p. s. i. across theY cylinder supply ports. In consequence, there is at all times, in the 'neutral spool position, ay preload of 1000 p'fs. i. on

bothsidesof the cylinder piston, thus preventing motion of theattached controlsurfa'ce under shocli'coliditions'. A minute movement of the spool of only aboutLOO in the case of the use of a first ow hole of .013 diameter for example, will close the normally bisected ilow holes on one side of the spool and open the other normally bisected holes. r,Then fluid ow to` one side of the pistonwill be made at a highly restricted rate as determined 'by the pressure and hole diameter so that the piston moves very slowly. Further motion of the spool will uncover more holes in the patterns on one side of the spool and close those on the other side so that an increasing but still restricted flow will be obtained to move the piston-faster.

In one specic example a neutral leakage hole .0l5"\in diameter and additional ow holes of the same diameter are used in each pattern. A neutral leakagel ow' of .02 G. P. M. through the bisected irst holes is obtained from the 2000 p. s. i. source. A maximum flow rate of from 3 to 5 G. P. M. can be obtained according to the number of ow holes used in each pattern as the spool is moved in either direction -so that the holes in lone pattern are completely open with the opposite h-oles completely closed. A spool travel of only about .125" from neutral is utilized, providing a full spool travel for the entire range of movement of the elevon of about .30. This travel is less than the stroke of valve operating rod 61.

In the preferred form of elevon motor shown in Figure 4, the valve operating rod 61 is spring loaded in both directions. This r-od, under all normal circumstances, acts as aV solid rod as far as the operation of the valve is con'- cerned, but as the spool travel in this preferred construction is about .125l in either direction and the quadrant travel may be several inches, it might be possible for the pilot to operatefhis control column faster -thanthe cylinder and piston could move the connected control surface. If .this `should happen, the spool would have full pilot force applied thereagainst, if rod 61 were solid. VBy spring loading this rod in both directions to permit change in length of about 50% ofthe quadrant travel, the spring load can be made so that when the rod lengthens or contracts, only a safe force is applied to the valve spoolv and block if the rate of pilot movement of the control is'greater than the rate of response of the hydraulic n1otor'.nl This spring loaded rod also'perniits full operation of onemotor unit when the valve spool of the `othermotor -unit =is jammed, and prevents damage .to the valve kspools if the pilots control element is operated without hydraulic pressure on the cylinder piston. v

In operation, it wi'll be noted `that as the cylinder is attached to the elevon operating arm and the piston rod to the wing, and as the valve and valve block is attached to the cylinder, with the valve operatingY rod 61 coming from the wing, no mechanical feed-back link is needed. With the valve operating rod 61 in neutral-position the elevon is held in neutral position by the preload mentioned above. When the valve operating rod 61 is moved away from neutral by the pilot the spool is moved and fluid is admitted to `one or the other sides of the piston, withy the ropposite side of the piston open to the fluid return. The cylinder then moves in accordance with the'pressure application, and the elevon is moved. As the elevonfmoves, however, the valve also moves as itis attachedqto the cylinder but the spool does not, as it is heldin position by the pilot. When the neutral point ofthe spool within the valve is reached the elevon movement stops, having moved away from neutral in accordance with pilot control movement. Thus, the cylinder and, consequently,-the elevon will follow all pilot initiated movement of the valve operating rod 61. The extremely short feed-back circuit created by the attachment of the valve to the cylinder with cylinder moving with the elevon eifectively prevents hunt.- ing. As the cylinder and valve casing are both attachedto the elevon and move with it, the follow-upmovernent of the -cylinder and valve casingis equal to the.initiating movement of the valve spool bythe pilot'.` `s tlie aero- -7 dy? 'fc ,espansa if elevon @varient is substantially linearly related to movement of the elevon, it is clear that .in this. construction the aerodynamic response will be substantially linearly related to movement Iof the pilots control.` m( o, I

WIn. certain types of airplanes, such as the all-wlng airplane shown in Figures l and 2, it is desirable to employ dragv type rudders 6 to achieve directional control, because of theab'sence of a tail section for mounting a conventional rudder.A Such drag rudders may take the 'form of hinged ilapssimultane'ously opened to project both above -andbel'ow the trailing edge of the wing, preferably near the tips thereof. Using such a split-flap rudder, a linear relation between pilots rudder pedal movement and rudder surface separation does not provide a linearly related amount of aerodynamic response. instead, there must be arr'ela'tivelylarge movement of the rudder surfaces near the closedposition toobtain a small aerodynamic response, changing into a small surface movement near the full open position for a large response. Since it is desired to provide alinear relation between rudder pedal movement and aerodynamic vresponse, a biased feed-back system is desirable for operation of the rudder surfaces.

:Full power operation of the rudder is accomplished by the pilot, operating the hydraulic servo valves of two power units, through a control cable from rudder pedals (not shown). asin the aileron control above described, to govern the opening and closing of the rudder flaps. As in the aileron system ypreviously described herein, the valve of each motor `of the pair controlling one set of rudder aps is actuated separately and directly from the rudder cables with across connection between the valves of the motors o'f each pair. o In order that each rudder pedal position will correspond to a denite surface position, a follow-up rod driven by the rudder is used to shut oif the servo valve when the correct surface separation is reached. The relation between rudder pedal displacement and surface movement is made non-linear by the fact that one end of` the follow-up describes a 'circular arc, while the other end traces a straight line, identical in part to the motion of a connecting'rod between a piston and crankshaft.

In Figure 6, diagrammatically showing one motor unit only `of the'pair used to control one rudder, each rudder fc'onsists of two panels or flaps 150 and 151, one mounted Von top of the other along the trailing edge of trim flap 3 (Figures 1 yand 2), with their forward ledges hinged to Vthe trim flap 3 along axes A and B respectively, so that when they are operated, one will rotate upwardly and the other will rotate downwardly, assuming the position` indicated bythe dotted lines X. The upper rudder ap 150 is rotated about itshinge line A by the action of la hydraulic rudder cylinder 152, the forward end of which is anchored to the aircraft structure 153. A piston rod 154'projects aft from the cylinder 152 and attaches to 'an operating arm `155mounted on the upper rudder 150. The other end of the piston rod 154 is connected to the customary piston 154a enclosed in the rudder actuating'cylinder 152. Hydraulic supply and return lines 156 and 157 are connected to the cylinder 152 on opposite sides of the enclosed piston 15451, so that uid pressure Mmay be made to extendvor retract the piston rodr154`and`t'her`eby operate the upper rudder flap 150.

Two'lopposingquadrants 16d) are installed in backto back'relation'ship, one on'thc upper rudder iap 150 and one on the lower rudder ap 151. Crossed'cables 1,61 are then connected, 'each with one end attached to the forward en'dfof each quadrant 160, and the other end attached to the aft endvof each quadrant, to'causethe Iowerlru'dder 151 to operate from the upper rudder 150, hutin't'heopposite direction. The hydraulic supply and return lines 156 and 157 connect to a rudder servo valve I1`t2hwhich controls theactuating cylinder 152.A Also connected to thevservo valve 162 is al hydraulic pressure Sllpplylinell'and a'ret'ur'n'line164 from the airplanes constantpressure hydraulic system. As in the previous 8 embodiment, valve spool is provided which; by 'its sition within the valve 162, determines which ofthe cylinder lines 156 or 157 is pressurized, or, which'nin the neutral position, applies a leakage pressure to both cylinder lines 156 and 157. Servo valve 162 is fixed to aircraft structure 153, while the valve spool is free to slide, within limits, in or out of the servo valve. The servo valve 162 may be similar to the example previously described except that it is attached to the aircraft structure instead of to the actuating cylinder. In addition, due to an increased airload it may be desirable to have lluid ow in the rudder valves approximately twice that used in the elevon valves. o v

Two rudder control cables 166 from one of the pilotos rudder pedals connect, one to each end of a cable lever 167 pivoted on a support shaft l midway between the ends. This support shaft 168 is mounted on a bracket 17o rmly attached to the aircraft structure 153. y A link pin connection 1,71 is provided on the cable lever 167, between shaft 168 and one of the cable attachments. To the link pin connection 171, a valve feed-back link 178 is rotatably attached approximately at its midpoint above the cable lever 167. One end 18u of the valve link 17S is connected by a spool rod 179 to the valve spool; this connection to link 17S being at a point preferably coaxial with the cable lever support shaft 168 when the servo valve spool is in the neutral position. The other end 181 of the valve link 178 is pinned to one end of a spring loaded follow-up rod ILSZ, which connects to a horn 153 that is firmly attached to the upper rudder 150, and projects forwardly and slightly downwardly from the hinge axis A.

ln the closed position of the rudder flaps, the followup rod 182 is not on a straight line with the hinge axis A, but is nearly so; the extended center line C of the follow-up rod 182 passing slightly beneath the hinge axis A.

The desired cross connection between the power units on each rudder is made in this case by attaching axle quadrants M and P to shaft 168 and connecting the quadrant M, by the cross connection cable L to the quadrant M of the other power unit assembly (not shown) exactly as set forth in the description of the cross connection between the two power units used for clcvon control.

When drag rudders 6 are used, it is customary to connect the rudder on one wing tip to its own operating pedal only, in order that both rudders may be opened simultaneously to obtain the desired bilateral drag, and this connection is followed in the system herein described.

In operation, when one rudder pedal is pushed by thc pilot, the cable lever 1t57 connected to that pedal rotates clockwise, as viewed from above, about its support shaft 168, displacing `the link pin connection 171 to thc right. This rotates the valve link 178 about the forward` end of the follow-up rod 132, which is yet stationar'y, and moves the spool rod 179 toward the servo valve 162, admitting fluid pressure to the proper end of the actuating cylinder 152 to separate the vrudders and 151. As the upper rudder 15h rotates about its hinge axis A, the horn 183 moves downwardly and to the rear, also about the same hinge axis A. The follow-up rod 182 is thus pulled to the rear, and now the valve link 178pivots about the link pin connection 171, which is stationary while the pedal is being held down. The valve link 17S, driven by the follow-up` rod 182, returns the valve spool to its neutral position, stopping the rudder surface movement. The servo valve 162is now closed and the rudders are held in some open position until subsequent movement of the cable lever 167. In a manner similar to that described, any surface position can be obtained by the proper amount of pedalldisplacement. y

As .the rod 182 and horn 183 are nearly in alignment at the beginning of rudder flap movement, the feed-back travel of rod 182 and connectedvvalvespool will be small` during the initial movement of the rudder surfaces.4v Thusv the rudder surfaces will separate a substantial distance before shutting o flow in valve 162. However, after the rudder surfaces have opened a substantialdistance the angle of horn 183 with rod 182 approaches 90 and the follow-up response approaches linearity. Thus, for a` given movement of the rudder pedal, movement of the rudder surfaces is greater near the closed `position than near the open position thereof.

This non-linearity is used to make the aerodynamic response of the surfaces substantially linear with movement of the rudder pedal. ln the XB-35 airplane described above, the aerodynamic response to rudder flap separation is small until the flaps are separated about 4 inches at their trailing edges. This initial separation can be made to take place with a very small pedal movement by use of the linkage described above.y

As each rudder pedal is moved` by pilot applied force in one direction only, follow-up rod 182 need benspring loaded in one directiony only. This spring loading will permit rod shortening under pilot force when a spool is jammed, will prevent pilot force being applied to valve 162 when no hydraulic pressure ispresent to move the rudder surfaces. in addition, the spring loaded rod will, particularly when used on rudders of the split-flap type described herein, permit the surfaces to be vforced back toward the closed position by air loads applied thereon when, for example, it would bepdangerous for the surfaces to be fully separated, such as at high speed.k This safety feature is accomplished by regulating the maximum applied hydraulic force to a valve where safe airloads on the surfaces cannot be exceeded. Under these circumstances, at this airload the surfaces will not kopen further. lf, however, the pilot should hold the valve wide open, and the airload should close the surfaces, the valve spool might bottom in the valve 162 so jthat the entire airload of the surfaces could be transmitted back to the pilot. To prevent this, the spring in rod 182 will compress upon an applied load of about 85 lbs.

As in the aileron system previously described, Vthe direct separate connection of each power unit valve Vto the rudder pedal with the described cross connection between valves, permits either of the rudder cables' to operate both valves in case of breakage'v of one of the rudder cable connectors.

While the present invention has been described `as being applied to the control of various surfaces" in airplanes of the all-wing type, itr obviously can'be utilized for the control of any airplane control surface where the aerodynamic restoring forces are large and where the aerodynamic response is either substantially linear or non-linear with surface movement. In eitherv casethe aerodynamic response can be made substantially linearly related to movements of the pilots control element.

VFrom the above descriptionit will also be clearly seen that the present invention makes possible the safe full power operation of airplane control surfaces irrespective of size or aerodynamic resistanceto motion. There is no feed-back of any kind from surface to pilot under normal conditions. The operation of the hydraulidcylinder requires only a few pounds of pilot effort, little more, in fact, than that required to overcome the overall resistance of the cable system and the control'neutrali'zing system. Neutralization of theV controls is performed by balanced elastic forces at the pilotslcation 'andthe overall pilot effort for normal piloting is small, irrespective of control surface.arearand'aerodynamic forces exerted thereon. The control forces maybe madeany desired magnitude or made to vary in most any desired manner. They may be laltered with ease after the airplane is own. Since the control forces can be made any desired magnitude, a control stickrather than a column and wheel becomes possible even 'on lar'g`e""ai'r planes, thus simplifying cockpit design and improving instrument visibility; t

As the control cablescarry only friction forces and are used to transmit a signal ratherthan a force, 'the cables may be very small in diameter with resulting decrease in friction, weight, and sensitivity to temperature changes.

A number of other advantages will be apparent to those skilled in the art. For example, trimming through the full range of surface travel is easily accomplished and can be done without loss of surface power that would normally result from the displacement of a' tab and emergency flight control and ground control locks become unnecessary. In addition, the present invention permits .the use of one surface to accomplish landing flap, dive brake, and aileron functions, for example, since erratically varying hinge moments will not cause erratic control forces.

Again, because of the relative simplicity as compared to a power boat system, and to the particular cross connections used, the fully powered system of the present invention is less vulnerable to damage in military use, and maintenance problems are reduced.

Reference has been made herein to the pilot of the airplane as being human. Obviously, however, when automatic piloting devices are used to take over control column movements, no diiference in results obtained by the present invention will be found. Thus, the term pilot as used in the appended claims will be deemed to include both human pilot and/ or automatic pilot devices. In fact, the low and uniform control forces required for fullpower operation of large control surfaces, as described herein, make the system readily adaptable to control by -automatic pilot mechanisms and the same power units can be used for normal and auto-pilot movement'of the surfaces. p

While in order to comply with the statute, the invention has been described in language more or less specific as to structural features, it is to be understood thatfthe invention is not limited to the specific features shown, but that the means Vand construction herein disclosed `comprise a'preferred form of putting the invention into effect, and the invention is therefore claimed in any of its forms or modiiications within the legitimate and valid scope of the appended claims.Y

What is claimed is:

l. In an airplane control system; an attitude control surface, a pair of separate surface actuating motors mounted adjacent said surface and operatively connected in parallel thereto, each of said motors having motor control means connected respectively thereto and `movable to control its respective motor, a pilots control element remote from. said motor control means, a separatel operating connection between each of said motor control means and said pilots control element, and a direct cross interconnection between said operating connections adjacent each of said control means, said operating connections and said interconnection ynormally acting simultaneously as a composite unit circuit when coutrolled by operation of said pilots control element.

`2. In an airplane control system; an attitude control surface, a pair of separate surface actuating motors mounted adjacent said surface and operatively connected in parallel thereto, each of said motors having motor control means connected respectively thereto and movable to control each said motor, a pilots control element remote from said motor control means, a separate and complete'operating connection between each of'said motor control means and said pilots control element, each of said operating connections including a normally rigid, preloaded resilient means adjacent said motor control means, and a direct cross interconnection between said operating connections, said interconnection being made to' the pilots control element end of each of said resilient means.

' 3. In an airplane control system; an attitude control surface, a'pair of separate* surface actuating motors mounted adjacent said surface and operatively. connected vparallel thereto, each of said motors lhfavin'g motor control m'leansconne'cted respectively thereto and vmovntrol each said xmotor, 'a pilots control element remote from y'said motor control means, a separate andcornplete operating connection between each of said niotorrcntrol means 'and said pilots control element, e'licli of said loperating 'connections including a normally rigid, `preloaded resilient :means adjacent lsaid motor Control means, an'd a direct cross in'terc'onnectionl between respective points of said operating connections adjacent the pilo'ts control element end of each of said e'silient means, said preloaded resilient means being yieldlmly under forces substantially in excess of normal nio or control means operating forces, and 'said resilient niean's being the only operating connections to said 'motor control means. l

y In an airplane 4control system; an attitude control surface, a pair 'of separate surface actuating motors frluntediadjacent said surface and yoperatively connected in parallel thereto, each of saidimotors having rnotor control meansI connected respectively thereto andlmovable 'to control each said motor, a pilots control element remote from said motor control means, a separate and complete operating connection between each yof said motor control means and said pilots control element, each lof said operating connections including a normally rig/id, 'preloaded resilient means adjacent said motor control means, and a direct cross interconnection between said 'operating connections at points thereof adjacent the pilots control element end of each of said resilient o meyans,`said preloaded resilient means being yieldable in bothdirections only under forces substantially/in excess of normal motor control means operating forces, and said vpreloaded resilient means being the only operating connections to said motor control means.

f5. In an airplane, a full powered system for operating an attitude control surface; comprising rst and second hydraulic motors operatively connected in parallel to said'surface to move said surface when energized, a source of fluid under pressure, first and second rhydraulic valves respectively adjacent and respectively connected to said first and second motors, said valves being movable to respectively energize said motors from said source, a pilots control element, a iirst valve operating means connected from said pilots control element to said first valve, a Second valve operating means connected from said pilots 'control element to said second valve, each of said valve operating means including normally rigid, preloaded resilient means adjacent to the valve to which the valve operating means is connected, andl a valve operating interconnection between said two resilient means at respective points adjacent the pilots control element ends of said resilient means, said valves being operable solely through said resilient means under all conditions.

6. In an airplane; a full powered system vfor operating an attitude control surface, comprising-first'and-second hydraulic motors operatively connected in parallel tosaid surface to move said surface when energized, a source of uid under pressure, rst land secondhydraulic valves respectively adjacent andvrespectiv/ely connected to said first and second motors, said valves being-'movable t o respectively energize s aid motorsfrom's'aid source, a pilots control'leleme'nt, a'first vvalve operating means connected from said pilots controlelement t'o l'sai'd rst valve, fa secondvalve operating means vconnectedfrom sfaid pilots control element to said secondvalve, each of'saidvalve operatingmeans including vnormally rigi'd, preloaded resilient means adjacent to the valve to which the valve operating means is connected, anda valvev operating interconnection betweein said two resilient means at respectivepoints adjacent thepilots'control element ends of `said resilient `means, said ypreloaded resilient ni'eans'being yie'l'dable in both directions and'being vthe s'le means of coupling pilots control element movement with said valves.A i

7. Inman airplane; a full powered system for operating anattitude 'control surface, comprising first and second hydraulic rn'otors operatively 'connected in parallel to said surface to move said surface when energized, a source of ud under pressure, first and second hydraulic Avalves respectively adjacent and respectively connected Yto said first 'and second motors, 'said valves being movable to respectively energize said motors from said source, a pilots control element, a first valve operating means connected from said pilots control element to said first valve, a second valve operating means connected 'from said pilots control element to said second v'alye, each 4'of said valve operating means including normallylrigid, preloaded resilient means adjacent to the valve to which the val'v'e operating means is connected, and a valve loperating interconnection between said two resilient means at points thereof adjacent the pilots control element ends thereof, said preloaded resilient means being yi'el'dable Iin both directions only under forces substantially 'greater than normal valve operating forces, and saidres'ilient means forming the only 4valve operating con` nections of said'system.

8. In an airplane control system; an attitude control surface, a pair of motors mounted adjacent said surface and 'operatively connected in Vparallel to said surface to move ,"s'aid surface, each of said motors having motor control fm'ea'ns connected respectively thereto, an operating connection directly between said two motor control means, a pilots control element, and a separate cornplete operating connection between said pilots control element and each of said motor control means.

9. In an airplane; a full powered system for operating anvattitude control surface, comprising first and second hydraulic motors operatively connected in parallel to said surface to move said surface when energized, `a source of -fluid under pressure, first and second hydraulic valves respectively adjacent `and respectively connected to said first and second motors, said valves being movable to energizel said motors from said source, a pilots control element, yalfirstvalve operating means connected only between said 'pilots -control element and said first valve, ya second valve operating means separately connected only between said pilots control element and said second valve, and avalve operating interconnection directly between said valves.

10. In an airplanera full powered system for operating an attitude control surface, comprising first and second hydraulic motors operatively connected inparallel to saidsurfaceto move said surface when energized, `a source of fluid under pressure, lirst and second hydraulic valves respectively 4adjacent 4and -respectively connected to said first and second-motors, said valves being -movable lto energize -said motors-fromsaid source, a pilots control element, Ifirst and second valve rods connected respectively to said first and second valves, a first valve operating means connected solely from said pilots control element to saidfirst valve operating rod, second valve Operating means 'independently connected solely from said pilots control element to said `second valve operating rod, and a complete rod operating interconnection solely between said two rods at Vpoints adjacent the respectiveconnections ofsaidvalve operating means thereto.

1,1. In an airplanecontrol system; an attitude control surface, a .pair of surface actuating motors mounted adjacent said surface Yand operatively connected in parallel thereto, each of said motors having motor control means connected yrespectively thereto, each of said motor control means having two relatively movable-parts, an operating link for each of said motor control means, each of said links being connected'at one end to one of said two relatively movable parts of a motor 'control means, a pilots controlele'ment remote from -said'motor control means, 'a separate operating connection between theother end of each link and said pilots control element, a feed-back connection between said surface `and each of the other parts of said motor control :.ieans, and an operating interconnection directly between said other ends of said two links, said links each including normally rigid, resilient means yieldable under a force greater than the force normally required to operate its respective connected motor control means, said resilient means being the only paths of control from said pilots control element to said motor control means.

12. Apparatus in accordance with claim 1l wherein said motors are hydraulic and have a cylinder connected to said surface and a piston connected to said `airplane and wherein said motor control means is a valve the two parts of which are a spool and a casing attached to said cylinder, and wherein said links are attached at one end to said spools and at the other ends to said operating connections.

13. Apparatus in accordance with claim 11 wherein said motors are hydraulic and have a cylinder connected to said surface and a piston connected to said airplane and wherein said motor control means is `a valve the two parts of which are a spool and a casing attached to said cylinder, and wherein said links are attached at one end to said spools and lat the other ends to said operating connections and wherein said resilient means is yieldable in two directions.

14. 1n a full powered airplane `attitude control system, an attitude control surface to be moved, two hydraulic motors operating in parallel to move said surface, each said motor including a hydraulic cylinder attached to said surface and ya hydraulic piston in said cylinder, said pistons being attached to said airplane, a separate valve casing mounted on each of said cylinders, a source of hydraulic fluid under pressure connected to each of said casings, a separate valve spool movable in each said casing to control iiuid energization of its respective motor, a pilots control element, a separate spool operating rod connected at one respective end thereof to each s-aid spool, the other respective ends of said rods being connected directly by separate linkage means to said pilots control element to be moved in unison by movement of said latter element, a rod operating cross connection between said other ends of said rods, the range of movement of the spool ends of said rods for full energization of said motors being less than the possible range of movement of the other ends of said rods by said pilots control element, and a separate normally rigid, preloaded resilient means forming a part of 4each said rod, each of said resilient means being yieldable only under a load substantially greater than normal spool operating loads, there being no other operating connection of said pilots control element to either of said valve spools than directly in series through the respective resilient means.

15. Means for controlling the operation of a pair of power-operated actuators connected in parallel to operate -a single movable output member in a full-power system, each or" said actuators having a movable control member, which comprises: a separate normally rigid, preloaded resilient means connected at one end to each of said control members, respectively, a manual control element remote from said actuator control members, a separate and complete mechanical operaivv` ig connection between said control element and each ot' the other respective ends of said two resilient means, and a direct operating interconnection between said other ends of said two resilient means, said preloaded resilient means being yieldable only under forces substantially in excess of normal operating forces of said control members, whereby either of said resilient means will yield if jammed and allow normal operation of the other to actuate said output member.

16. Means for controlling the operation of a pair of hydraulic power actuators connected in parallel to operate a single control surface in a full-power system, each of said actuators having a feed-back connection thereto from said surface, a control valve and a movable valve control rod operatively attached thereto, which comprises: a pair of double-acting, normally rigid, preloaded resilient means connected at one end of each to one of s-aid control rods, respectively, a manual control element remote from said control rods, a separate and complete operating connection from said control element to each respective other end of said resilient means so that said resilient means form the only paths of control transmittal from said control element to said control rods, and a complete operating interconnection directly between said resilient means other ends, said resilient means being yieldable in both directions only under forces substantially greater than normal control rod operating forces.

17. Apparatus in accordance with claim 16 including a source of hydraulic uid under pressure connected to said control valve, the range of movement of said control rods in said valves for full energization of said actuators being only a small fraction of the possible range of movement of said manual control element for full deliection of said surface, and wherein said entire controlling means has a hydraulic Stalling and reversal point under unsafe loads on said surface, said resilient means being yieldable after said valve control rod is bottomed at the end of its range due to said reversal.

References Cited in the le of this patent UNITED STATES PATENTS 949,559 Wilson Feb. 15, 1910 1,339,332 Greenly May 4, 1920 1,763,590 Klemperer June 10, 1930 2,315,110 Dornier Mar. 30, 1943 2,360,542 Berry Oct. 17, 1944 2,366,382 Burton et al lan. 2, 1945 2,395,671 Kleinhans et al Feb. 26, 1946 2,613,890 Beman Oct. 14, 1952 2,616,264 Grant et al Nov. 4, 1952 2,619,304 Feeney et al Nov. 25, 1952 2,620,772 McLane Dec. 9, 1952 2,640,466 Fceney lune 2, 1953 FOREIGN PATENTS 480,528 Canada Jan. 22, 1952 582,380 Great Britain Nov. 13, 1946 

